Various flap bearing systems in motor vehicles have previously been described. Particularly in flaps arranged in thermally stressed areas, it is desired to achieve a good heat dissipation on the side of engagement by the actors in order to protect adjusters, particularly electric adjusters, from overheating. For this reason, particularly in exhaust gas flaps, use is made of flap bearing systems whose bearings are, toward the outside, not fully arranged in a closed housing but are formed partially open toward the outside. This has the effect that the heat transported via the flap shaft can be at least partially dissipated via the surroundings.
These flap bearing systems must further be suited to compensate for thermal expansion in the valve shaft or the bearing sites so as to safeguard the smooth running of the flap shaft. For this purpose, it is required to avoid depositions on the flap shaft in the area of the bearing support to the largest possible extent. Various measures have consequently become known to effect a good inner and outer sealing tightness at the flap valve bearing site.
DE 195 26 144 A1 and DE 100 06 795 A1, for example, describe an arrangement of the throttle flap whose flap shaft is supported, on its side facing toward the actuator, via a radial bearing arranged in a bearing housing. An axial bearing washer is additionally arranged in the bearing housing for sealing purposes, which, having a corresponding shape, is arranged in abutment against a conical shoulder of the flap shaft. This axial bearing washer is pressed against an axial wall enclosing the bearing housing, wherein, to this effect, a pressure spring is arranged to bias the shaft and thus the shaft shoulder towards the axial wall. The spring is surrounded by a sleeve extending beyond the edge of the bearing housing.
DE 37 07 904 A1 describes a flap valve for an exhaust gas conduit whose shaft is supported in a ceramic sleeve having a calotte-shaped outer contour via which the sleeve is pressed, in a spring-loaded manner, into a correspondingly shaped bearing housing portion. The bearing housing portion receiving the sleeve is largely, but not fully, closed by a cover.
These valve bearing systems are effective to reduce, by means of the sleeve, the quantity of splash water to which the bearing site is exposed during operation. However, ingress of splash water cannot be entirely prevented because, since thermal stresses will cause different degrees of expansion of the materials, a gap must be provided between the bearing housing and the sleeve to prevent component parts from grinding against or getting caught with each other. As a result, however, splash water can intrude into the bearing area via the gap, become distributed along the shaft and, inter alia because of thermal stresses, will evaporate there resulting in deposits between the shaft and the bearing that may lead to a malfunction. Once water has intruded into this area, this water cannot be easily removed from the bearing area due to the relatively small gap and therefore will remain in the interior.